With the advent of extended range electric vehicles, users are given the mechanical simplicity and energy efficiency of electric-only drive without losing the range and energy security of fuel-based systems. As used herein, the term “extended range electric vehicle” refers to a vehicle that is propelled by one or more electric motors linked to the vehicle drive wheel or wheels, wherein the electric energy used to power the motors is stored in an onboard battery system, and wherein an onboard auxiliary power unit, e.g., a gasoline or diesel engine, powers an onboard generator to supply additional electrical energy to the onboard battery system.
In this way, a smaller onboard battery system may be used without risking stranding the vehicle owner once the battery energy is depleted. Moreover, since the onboard auxiliary power unit only drives a generator and need not be linked to the drive wheels directly, the use of gearing, clutches and other mechanical power transmission systems can be minimized. Typically, the primary charging source for an extended range electric vehicle is a stationary power source such as a plug-in receptacle, used while the vehicle is not in use, e.g., overnight or during the work day.
However, a user may not necessarily remember to plug in their vehicle when they have finished using it for a time, nor does the vehicle always need to be plugged in. For example, if the vehicle has not been used or has been used very little the previous day, the vehicle may not need to be charged. Moreover, even when the vehicle battery system is in need of charging, a reminder to that effect is of no use if the user is not in a location where the vehicle can be parked and charged. Thus, such reminder systems can be a substantial annoyance to the user.
Moreover, although extended range electric vehicles provide range security by way of the auxiliary power unit, many users will still desire to engage in electric only driving, i.e., without using auxiliary power, to the extent possible. However, it is not always possible for a user to know whether a planned excursion will extend beyond the electric only range of the vehicle. For example, if a vehicle has an electric-only range of 40 miles, then a round trip excursion that is 21 miles one-way will require auxiliary power before the user is back at the starting point where they can plug the vehicle in to the stationary power source. Thus, a system of providing battery charge state clarity and predictability is needed.